Adding Caching Adapter, allows caching of _Role and _User queries (fixes #168) (#1664)

* Adding Caching Adapter, allows caching of _Role and _User queries.

src/Adapters/Cache/InMemoryCache.js

@@ -0,0 +1,66 @@
+const DEFAULT_CACHE_TTL = 5 * 1000;
+
+
+export class InMemoryCache {
+  constructor({
+    ttl = DEFAULT_CACHE_TTL
+  }) {
+    this.ttl = ttl;
+    this.cache = Object.create(null);
+  }
+
+  get(key) {
+    let record = this.cache[key];
+    if (record == null) {
+      return null;
+    }
+
+    // Has Record and isnt expired
+    if (isNaN(record.expire) || record.expire >= Date.now()) {
+      return record.value;
+    }
+
+    // Record has expired
+    delete this.cache[key];
+    return null;
+  }
+
+  put(key, value, ttl = this.ttl) {
+    if (ttl < 0 || isNaN(ttl)) {
+      ttl = NaN;
+    }
+
+    var record = {
+      value: value,
+      expire: ttl + Date.now()
+    }
+
+    if (!isNaN(record.expire)) {
+      record.timeout = setTimeout(() => {
+        this.del(key);
+      }, ttl);
+    }
+
+    this.cache[key] = record;
+  }
+
+  del(key) {
+    var record = this.cache[key];
+    if (record == null) {
+      return;
+    }
+
+    if (record.timeout) {
+      clearTimeout(record.timeout);
+    }
+
+    delete this.cache[key];
+  }
+
+  clear() {
+    this.cache = Object.create(null);
+  }
+
+}
+
+export default InMemoryCache;